java - Mysql数据库异常

Question

线程“主”java.lang.Error 中的异常: Unresolved 编译问题: 类型不匹配:无法从 java.sql.Statement 转换为 com.mysql.jdbc.Statement

i am a beginner in java i am trying to use mysql database i have downloaded mysql-connector-java-5.1.23-bin.jar file from mysql.com and i have added this jar file to in my build path of my project but there is an error in the following code Exception in thread "main" java.lang.Error: Unresolved compilation problem: Type mismatch: cannot convert from java.sql.Statement to com.mysql.jdbc.Statement

---

package com.example.demo;

import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;

public class DBConnect
{
private static final String userName = "root";
private static final String userpwd = "sverma";
private static final String CONN_STR = "jdbc:mysql://localhost:3306/phpweb_db";

public static void main(String[] args) throws SQLException
{

    Connection conn = null;
    Statement st = null;
    ResultSet rs = null;

    try
    {
        DriverManager.getConnection(CONN_STR, userName, userpwd);
        st=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
        rs = st.executeQuery("select * from user");
        rs.last();
        System.out.println("No of rows: " + rs.getRow());

        // System.out.println("Connected Successfully...");
    }
    catch (SQLException e)
    {
        System.err.println(e);

    }
    finally
    {
        if (rs != null)
        {
            rs.close();
        }
        if (st != null)
        {
            st.close();
        }
        if (conn != null)
        {
            conn.close();
        }
    }
}

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Answer 1

错误的类

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;

应该是

import java.sql.Connection;
import java.sql.Statement;

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事实上，java将一切都与特定的数据库引擎解耦了。永远不需要导入 MySQL(或 ProgressSQL 或...)类。

为了让这些类在运行时可用，在 try 之后，在获得连接之前的第一件事是:

Class.forName("com.mysql.jdbc.Driver");

这种技术将允许从配置文件中读取所有字符串，并编写与数据库无关的代码。

---

缺少:conn = ...

conn = DriverManager.getConnection(CONN_STR, userName, userpwd);